Bone treatment systems and methods

ABSTRACT

The invention provides instruments and methods for prophylactic treatment of an osteoporotic vertebral body or for treating a vertebral compression fracture (VCF). In one exemplary method, a probe system uses a high speed rotational cutter for abrading or cutting a plane within vertebral cancellous bone. Optional irrigation and aspiration sources are included in the probe system for removing abraded bone debris. In one embodiment, the high speed cutter uses a tissue-selective abrading surface that abrades or cuts bone but does not cut soft tissue. After the creation of a weakened cut plane in the bone, reduction of the fracture requires reduced forces.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of Provisional U.S. Patent Application Ser. No. 60/629,628 filed Nov. 19, 2004 titled Systems and Methods for Treating Vertebral Fractures. This application also is related to U.S. application Ser. No. 11/165,652 filed Jun. 24, 2005 titled Bone Treatment Systems and Methods; and U.S. patent application Ser. No. 11/165,651 filed Jun. 24, 2005, titled Bone Treatment Systems and Methods. The entire contents of all of the above cross-referenced applications are hereby incorporated by reference in their entirety and should be considered a part of this specification.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to medical devices, and more particularly to methods and apparatus for treating an abnormal vertebra. More particularly, an apparatus and method includes using a probe carrying a tissue-selective elastomeric rotational cutter having an abrasive surface for cutting a plane within vertebral cancellous bone to create a weakened plane.

2. Description of the Related Art

Osteoporotic fractures are prevalent in the elderly, with an annual estimate of 1.5 million fractures in the United States alone. These include 750,000 vertebral compression fractures (VCFs) and 250,000 hip fractures. The annual cost of osteoporotic fractures in the United States has been estimated at $13.8 billion. The prevalence of VCFs in women age 50 and older has been estimated at 26%. The prevalence increases with age, reaching 40% among 80-year-old women. Medical advances aimed at slowing or arresting bone loss from aging have not provided solutions to this problem. Further, the affected population will grow steadily as life expectancy increases. Osteoporosis affects the entire skeleton but most commonly causes fractures in the spine and hip. Spinal or vertebral fractures also have serious consequences, with patients suffering from loss of height, deformity and persistent pain which can significantly impair mobility and quality of life. Fracture pain usually lasts 4 to 6 weeks, with intense pain at the fracture site. Chronic pain often occurs when one level is greatly collapsed or multiple levels are collapsed.

Postmenopausal women are predisposed to fractures, such as in the vertebrae, due to a decrease in bone mineral density that accompanies postmenopausal osteoporosis. Osteoporosis is a pathologic state that literally means “porous bones”. Skeletal bones are made up of a thick cortical shell and a strong inner meshwork, or cancellous bone, of collagen, calcium salts and other minerals. Cancellous bone is similar to a honeycomb, with blood vessels and bone marrow in the spaces. Osteoporosis describes a condition of decreased bone mass that leads to fragile bones which are at an increased risk for fractures. In an osteoporotic bone, the sponge-like cancellous bone has pores or voids that increase in dimension, making the bone very fragile. In young, healthy bone tissue, bone breakdown occurs continually as the result of osteoclast activity, but the breakdown is balanced by new bone formation by osteoblasts. In an elderly patient, bone resorption can surpass bone formation thus resulting in deterioration of bone density. Osteoporosis occurs largely without symptoms until a fracture occurs.

Vertebroplasty and kyphoplasty are recently developed techniques for treating vertebral compression fractures. Percutaneous vertebroplasty was first reported by a French group in 1987 for the treatment of painful hemangiomas. In the 1990's, percutaneous vertebroplasty was extended to indications including osteoporotic vertebral compression fractures, traumatic compression fractures, and painful vertebral metastasis. In one percutaneous vertebroplasty technique, bone cement such as PMMA (polymethylmethacrylate) is percutaneously injected into a fractured vertebral body via a trocar and cannula system. The targeted vertebrae are identified under fluoroscopy. A needle is introduced into the vertebral body under fluoroscopic control to allow direct visualization. A transpedicular (through the pedicle of the vertebrae) approach is typically bilateral but can be done unilaterally. The bilateral transpedicular approach is typically used because inadequate PMMA infill is achieved with a unilateral approach.

In a bilateral approach, approximately 1 to 4 ml of PMMA are injected on each side of the vertebra. Since the PMMA needs to be forced into cancellous bone, the technique requires high pressures and fairly low viscosity cement. Since the cortical bone of the targeted vertebra may have a recent fracture, there is the potential of PMMA leakage. The PMMA cement contains radiopaque materials so that when injected under live fluoroscopy, cement localization and leakage can be observed. The visualization of PMMA injection and extravasion are critical to the technique—and the physician terminates PMMA injection when leakage is evident. The cement is injected using small syringe-like injectors to allow the physician to manually control the injection pressures.

Kyphoplasty is a modification of percutaneous vertebroplasty. Kyphoplasty involves a preliminary step that comprises the percutaneous placement of an inflatable balloon tamp in the vertebral body. Inflation of the balloon creates a cavity in the bone prior to cement injection. Further, the proponents of percutaneous kyphoplasty have suggested that high pressure balloon-tamp inflation can at least partially restore vertebral body height. In kyphoplasty, it has been proposed that PMMA can be injected at lower pressures into the collapsed vertebra since a cavity exists to receive the cement—which is not the case in conventional vertebroplasty.

The principal indications for any form of vertebroplasty are osteoporotic vertebral collapse with debilitating pain. Radiography and computed tomography must be performed in the days preceding treatment to determine the extent of vertebral collapse, the presence of epidural or foraminal stenosis caused by bone fragment retropulsion, the presence of cortical destruction or fracture and the visibility and degree of involvement of the pedicles. Leakage of PMMA during vertebroplasty can result in very serious complications including compression of adjacent structures that necessitate emergency decompressive surgery.

Leakage or extravasion of PMMA is a critical issue and can be divided into paravertebral leakage, venous infiltration, epidural leakage and intradiscal leakage. The exothermic reaction of PMMA carries potential catastrophic consequences if thermal damage were to extend to the dural sac, cord, and nerve roots. Surgical evacuation of leaked cement in the spinal canal has been reported. It has been found that leakage of PMMA is related to various clinical factors such as the vertebral compression pattern, and the extent of the cortical fracture, bone mineral density, the interval from injury to operation, the amount of PMMA injected and the location of the injector tip. In one recent study, close to 50% of vertebroplasty cases resulted in leakage of PMMA from the vertebral bodies. See Hyun-Woo Do et al, “The Analysis of Polymethylmethacrylate Leakage after Vertebroplasty for Vertebral Body Compression Fractures”, Jour. of Korean Neurosurg. Soc. Vol. 35, No. 5 (5/2004) pp. 478-82, (http://www.jkns.or.kr/htm/abstract.asp?no=0042004086).

Another recent study was directed to the incidence of new VCFs adjacent to the vertebral bodies that were initially treated. Vertebroplasty patients often return with new pain caused by a new vertebral body fracture. Leakage of cement into an adjacent disc space during vertebroplasty increases the risk of a new fracture of adjacent vertebral bodies. See Am. J. Neuroradiol. 2004 February; 25(2): 175-80. The study found that 58% of vertebral bodies adjacent to a disc with cement leakage fractured during the follow-up period compared with 12% of vertebral bodies adjacent to a disc without cement leakage.

Another life-threatening complication of vertebroplasty is pulmonary embolism. See Bernhard, J. et al., “Asymptomatic diffuse pulmonary embolism caused by acrylic cement: an unusual complication of percutaneous vertebroplasty”, Ann. Rheum. Dis. 2003; 62:85-86. The vapors from PMMA preparation and injection are also cause for concern. See Kirby, B., et al., “Acute bronchospasm due to exposure to polymethylmethacrylate vapors during percutaneous vertebroplasty”, Am. J. Roentgenol. 2003; 180:543-544.

Another disadvantage of PMMA is its inability to undergo remodeling—and the inability to use the PMMA to deliver osteoinductive agents, growth factors, chemotherapeutic agents and the like. Yet another disadvantage of PMMA is the need to add radiopaque agents which lower its viscosity with unclear consequences on its long-term endurance.

In both higher pressure cement injection (vertebroplasty) and balloon-tamped cementing procedures (kyphoplasty), the methods do not provide for well controlled augmentation of vertebral body height. The direct injection of bone cement simply follows the path of least resistance within the fractured bone. The expansion of a balloon also applies compacting forces along lines of least resistance in the collapsed cancellous bone. Thus, the reduction of a vertebral compression fracture is not optimized or controlled in high pressure balloons as forces of balloon expansion occur in multiple directions.

In a kyphoplasty procedure, the physician often uses very high pressures (e.g., up to 200 or 300 psi) to inflate the balloon which first crushes and compacts cancellous bone. Expansion of the balloon under high pressures close to cortical bone can fracture the cortical bone, or cause regional damage to the cortical bone that can result in cortical bone necrosis. Such cortical bone damage is highly undesirable and results in weakened cortical endplates.

Kyphoplasty also does not provide a distraction mechanism capable of 100% vertebral height restoration. Further, the kyphoplasty balloons under very high pressure typically apply forces to vertebral endplates within a central region of the cortical bone that may be weak, rather than distributing forces over the endplate.

There is a general need to provide systems and methods for use in treatment of vertebral compression fractures that provide a greater degree of control over introduction of bone support material, and that provide better outcomes. Embodiments of the present invention meet one or more of the above needs, or other needs, and provide several other advantages in a novel and non-obvious manner.

SUMMARY OF THE INVENTION

The invention provides systems and methods for treatment of vertebral compression fractures as well as systems and methods for prophylactic treatment of osteoporotic vertebrae in subjects having vertebrae that are susceptible to a compression fracture. The invention also can be used in correcting and supporting bones in other abnormalities such as bone tumors and cysts, avascular necrosis of the femoral head and tibial plateau fractures.

In one embodiment, a probe system is provided that has a working end comprising an elastomeric abrasive cutter that is rotated at high speeds by a motor drive. The rotational elastomeric abrader has a tissue-selective abrading surface that within a selective rpm range can abrade or cut cancellous bone or cortical bone but will not cut soft tissue. The system is used for abrading or cutting at least one path or space within vertebral cancellous bone. Irrigation and aspiration sources are included in the probe system for removing abraded bone debris. After the creation of a path or space in bone, an in-situ hardenable bone cement volume is introduced into each path or space to support the vertebra.

In another embodiment of the invention, a probe system has a working end that comprises an expandable structure having an abrasive surface. In use, the expandable abrading surface is rotated at high speed to cut bone while being expanded to increase the cross section of the path or space being created. The use of the expandable cutter allows the treatment of bone with low pressures to create paths or spaces without explosive expansion forces known in prior art balloon procedures that are designed to crush and compact cancellous bone in a vertebra.

There is a general need to provide systems and methods for use in treatment of vertebral compression fractures that provide a greater degree of control over introduction of bone support material, and that provide better outcomes. The present invention meets this need and provides several other advantages in a novel and nonobvious manner.

These and other objects of the present invention will become readily apparent upon further review of the following drawings and specification.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to better understand the invention and to see how it may be carried out in practice, some preferred embodiments are next described, by way of non-limiting examples only, with reference to the accompanying drawings, in which like reference characters denote corresponding features consistently throughout similar embodiments in the attached drawings.

FIG. 1 is a perspective schematic view of an exemplary system of the invention with an elastomeric tissue-discriminating cutter for abrading and cutting bone in an abnormal vertebra.

FIG. 2A is a sectional view of a vertebra with an elastomeric cutter similar to that of FIG. 1 being advanced over a straight guide member to abrade a path in cancellous bone.

FIG. 2B is a sectional view of an abnormal vertebra with another flexible shaft elastomeric cutter similar to that of FIG. 1 being advanced over at least one curved shape memory guide member to abrade a plurality of paths in cancellous bone.

FIG. 3 is a view of the abnormal vertebra of FIG. 2B with the plurality of path in cancellous bone infilled with a hardenable bone cement to reinforce the vertebra.

FIG. 4A is a sectional view of another vertebra with a flexible shaft elastomeric cutter similar to that of FIGS. 1 and 2B being used to abrade cortical bone to create a weakened plane.

FIG. 4B is a side view of the vertebra of FIG. 4A showing the method of abrading and cutting holes in cortical bone to create a weakened cortical bone region.

FIG. 5 is a sectional view of another vertebra showing a method of using the elastomeric cutter of FIG. 1 to abrade and cut a plane in cancellous bone of a vertebra.

FIG. 6 is a perspective schematic view of the working end and elastomeric abrasive cutter of an alternative embodiment wherein the cutter is expandable in transverse section.

FIG. 7 is a sectional view of an alternative working end and elastomeric abrasive cutter that is expandable in transverse section.

FIG. 8 is a sectional view of an alternative working end with a fluid-expanded elastomeric abrasive cutter that is expandable in transverse section.

FIGS. 9A-9D are sequential views of an fluid-expandable elastomeric cutter being used to abrade a space in cancellous bone, for example, in a vertebra.

FIG. 10A is a perspective view of an alternative working end with first and second rotatable abrasive cutter portions that are configured to extend in a plane relative to the instrument axis to create a weakened plane in bone.

FIG. 10B is a view of the working end of FIG. 10A in a method of use to abrade and cut a weakened plane in a vertebral cancellous bone.

FIG. 11 is a cut-away of an alternative flexible cutter as if taken along line 11-11 of FIG. 10A.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic view of an exemplary bone cutting system or probe 100 that has handle portion 102 that transitions to elongated extension member 104 that extends along axis 105. The extension member 104 carries a distal working end 110 that comprises a high speed elastomeric, abrasive rotational cutter indicated at 112. The handle portion 102 can be any suitable assembly for gripping with a human hand and can carry trigger and actuator mechanisms known in the art.

In the embodiment of FIG. 1, the elastomeric abrasive cutter 112 is fixedly coupled to the distal end of elongated drive member 114 that is rotated at a high speed by a rotation mechanism, such as an air motor or electric motor indicated at 115. The drive member 114 rotates in bore 118 in an elongated rigid sleeve 120 that is coupled to handle portion 102. The elongated sleeve 120 and elastomeric cutter 112 are configured with dimensions suited for insertion into a vertebra from a posterior transpedicular or extrapedicular approach, with the diameter of the sleeve 120 and cutter 112 ranging between about 1.0 mm and 4.0 mm, and more preferably between 1.5 mm and 3.0 mm. The length of the cutter 112 ranges from 1 mm to 10 mm, and more preferably from 2 mm to 5 mm. Of particular interest, the elastomeric cutter 112 is fabricated of a resilient polymer (e.g., silicone or urethane) that is embedded with abrasive crystals 122 or the like, for example diamond or other similar particles having a mean cross-section ranging between about 1 micron and 100 microns, and more preferably between about 5 microns and 50 microns. The rotation mechanism or motor 115 is configured for rotating the elastomeric cutter 112 at speed ranging from about 500 rpm to 400,000 rpm, and more preferably at speeds ranging between about 5,000 rpm and 100,000 rpm.

In the embodiment of FIG. 1, the drive member 114 has a bore 128 therethrough that allows the probe 100 to be advanced over a guide member such as a wire (not shown). The bore 128 also optionally can be used for fluid infusion to irrigate the site, and for this reason a fluid source 140 is shown in FIG. 1. As also shown in FIG. 1, the probe or system 100 optionally includes a negative pressure source 145 operatively connected to bore 118 in sleeve 120 for aspirating fluid and abraded bone debris from the bone treatment site. The distal end portion of sleeve 120 can have ports 148 or openings therein to allow fluid and bone debris to be aspirated into bore 118 of sleeve 120.

The elastomeric cutter 112 can be operated within a selected speed range that preferentially abrades and cuts bone such as cancellous or cortical bone but will not abrade soft tissue. This aspect of the invention is useful, for example, in operations in the interior of a vertebral body, for example when cutting through a cortical wall and inadvertently contacting soft tissue outside the vertebra. The system will discriminate tissue density and not cut the lower density soft tissue such as ligaments. The use of a resilient cutter at selected speeds to discriminate in cutting harder tissue and sparing softer tissue was disclosed in U.S. Pat. Nos. 4,445,509 and 4,990,134 to David C. Auth, which are incorporated herein by this reference. The Auth patents relate to endovascular catheter tips that are abrasive for cutting occlusive materials that clog an artery. The present invention is fabricated in the configuration of a rigid probe 100 with dimensions suited for percutaneous insertion into an abnormal vertebra.

In one method of use shown in FIGS. 2A and 2B, an elastomeric cutter 112 similar to the embodiment shown in FIG. 1 can be used to cut one or more straight or curved paths in cancellous bone 149 in vertebral body 150. In FIG. 2A, cutter 112 is advanced over a selected straight guide member 152. FIG. 2B illustrates cutter 112 advanced over a curved shape memory alloy guide member 154. In this embodiment, the bore 128 in drive member 114 is dimensioned to slide and rotate relative to the guide member 152 or 154. In the embodiment of FIG. 2B, the drive member 114 can be a helical drive element or braided sleeve that is flexible for rotating the cutter 112. In FIGS. 2A-2B, a plurality of paths 155 can be cut or abraded by this means with the result shown in FIG. 3. In FIG. 3, the plurality of paths 155 are then filled with a bone cement 158 (e.g., PMMA) injected through introducer sleeve 159. The bone cement 158 is adapted to prophylactically treat a vertebra 150 that may be susceptible to a compression fracture.

In FIGS. 4A-4B, another use of elastomeric cutter 112 is shown wherein tip 160 of the cutter is penetrated through the cortical bone wall 162 of vertebra 150 in at least one location 164 to create a weakened region. This use of the cutter will provide a fracturable region or line 165 in the cortical bone (FIG. 4B) that will allow for elevation of vertebral endplate 166 a relative to endplate 166 b upon the pressurized introduction of bone fill materials. This use of cutter 112 as indicated in FIGS. 4A-4B is adapted for cases in which a vertebral compression fracture has healed in a collapsed position with the bone portions fusing together. The cutter 112 thus allows cutting through cortical bone 162 with the cutter abrading bone but discriminating tissue based on density differences so that the cutter does not cut the ligaments 168 as the cutter tip 160 penetrates cortical bone layer 162. (FIG. 4A). This method of creating a weakened plane or region 165 in cortical bone was disclosed by the authors in U.S. Provisional Patent Application Ser. No. 60/622,209 filed Oct. 26, 2004 titled Systems and Methods for Treating Vertebral Fractures, which is incorporated herein by this reference and made a part of this specification.

FIG. 5 depicts another use of elastomeric cutter 112 in a vertebra wherein the working end 110 of the probe 100 is moved laterally and/or translated axially while rotating the elastomeric cutter 112 to abrade and cut a plane P. It can be understood that the cutting can be done from one or more access paths to the interior of the vertebra 150 to cut a suitable plane P. After cutting plane P, a bone fill material (e.g., PMMA) can be introduced in the plane P and increasing injection pressures of the bone fill material can be used to apply forces to move the endplates apart to reduce the fracture.

FIG. 6 depicts another probe 180 with an elastomeric cutter 112 similar to that of FIG. 1. In this embodiment, the motor-driven drive member 184 also functions as a pull-rod to axially compress and move the elastomeric cutter 112 to the shape indicated at 112′ wherein the transverse section of the cutter is increased to thereby abrade or cut a larger diameter path in cancellous bone. In this embodiment, the cutter 112 can be an elastomeric monolith of silicone, urethane or the like that is bonded to drive member 184. It can be understood that the proximal end 186 of cutter 112 will be pushed against the distal end 188 of sleeve 120 to thereby outwardly expand the transverse section of the monolith. In the embodiment of FIG. 6, a central bore in the probe is not shown as in bore 128 in FIG. 1, but such a feature is optional.

FIG. 7 is a sectional view of another probe 190 with an elastomeric cutter 112 that is similar to that of FIG. 6. In the embodiment of FIG. 7, the motor-driven drive member 184 again functions as a pull-rod to actuate elastomeric cutter 112 to an enlarged transverse section. In this embodiment, the cutter 112 is hollow to allow greater expansion than the version of FIG. 6. It can be seen that elastomeric cutter 112 has first and second ends, 191 a and 191 b, that are bonded to first and second collars 192 a and 192 b that cooperate with drive shaft 184. The second collar is bonded to shaft 184 and the first collar included projecting key elements 194 that slide in key slots 196 to key the rotation of cutter 112 to that of the shaft 184. In all other respects, the system operates as described above. In another embodiment (not shown) the wall 198 of the elastomeric cutter 112 has a plurality of perforations and the interior opening communicates with aspiration ports in a hollow drive shaft and/or in the introducer sleeve. It can be easily understood that an aspiration source and irrigation source as in probe 100 of FIG. 1 can be incorporated into a system using a mechanically expandable elastomeric cutter 112 having a perforated wall.

FIG. 8 is a perspective sectional view of an alternative probe 200 that carries a rotatable elastomeric cutter 112 that is fluid expandable, for example, by inflow of a liquid or a gas from any suitable pressure source 210. The elastomeric cutter 112 has a substantially thick expandable wall 212 that carries diamond abrasives as described previously. The expandable wall is coupled to shaft 220 having a lumen 232 extending therethrough to deliver fluid from the pressurized source 210 to a chamber 242 in the expandable cutter 112. The shaft 220 can be a flexible polymer, a superelastic alloy or the like. As described previously, the probe can have a bore extending therethrough (not shown) for advancing over a straight or curved guide member. A plurality of differently shaped guide members can be used as shown in FIGS. 2B and 3 to create varied geometry paths.

In another embodiment similar to that of FIGS. 7 and 8, an expandable, elastomeric cutter 112 can be a resilient polymer without an inflation chamber that is expanded by centrifugal forces resulting from very high rotational speeds, for example 50,000 rpm or higher and can be driven by an air motor. In another embodiment, the wall of a similar balloon structure is expandable but can still be fluid-permeable to allow leakage of saline or sterile water into the bone being abraded. An aspiration source can be coupled to such a working end as described above.

FIGS. 9A-9D illustrate an alternative method wherein a fluid-expandable structure with an abrasive surface as in FIGS. 7 and 8 is used to create a space 240 (or multiple spaces) in cancellous bone 149 to receive a volume of bone cement. On aspect of the method includes abrading a space in a bone and injecting bone cement under high pressure to distract cortical endplates to restore vertebral height. In one embodiment, the bone cement is the type described in co-pending U.S. application Ser. Nos. 11/165,651 and 11/165,652 filed Jun. 24, 2005, both titled Bone Treatment Systems and Methods, wherein the bone cement can be altered in viscosity on demand with the application of energy to prevent cement extravasion.

The method of FIGS. 9A-9D provides safe means for creating a space 240 in a bone, for example a substantially large space in vertebral cancellous bone to receive a bone cement. In one prior art method known as kyphoplasty as described above the section titled “Description of The Related Art”, a balloon is inserted in a cut or fractured path in cancellous bone 149 and then inflated with very high pressures. When inflating such a balloon, the bone structure acts akin to any ceramic material and only fractures under very large loads (e.g. up to 300 psi or more in the balloon)—at which time the fracture of cancellous bone is explosive. In kyphoplasty, the balloon is entirely constrained by the small path in cancellous bone until ever-increasing pressure fractures the cancellous bone resulting in “explosive” expansion of the balloon. The explosive expansion of a kyphoplasty balloon can cause point loading where the balloon contacts the cortical endplates of the vertebra. The explosive expansion of the balloon can easily crack an endplate if the expanded balloon wall is in close proximity to the endplate. When imaging the use of such a balloon device, it has been observed that the balloon moves explosively from a substantially collapsed condition to a fully expanded condition in an interval of less than a fraction of a second—the interval believed to be less than about one tenth of a second.

In contrast, the method of the invention depicted in FIGS. 9A-9D it is believed for the first time performs “non-explosive” balloon expansion with the interior of a vertebra by configuring the fluid-expandable structure with high speed rotational abrading functionality. At the same time, the inventive system removes bone debris by means of irrigation and aspiration to prevent the crushing and compaction of cancellous bone. The fluid-expandable structure 112 of FIGS. 9A-9C can be configured with an pressure source and controller so that the expandable structure is expanded with (i) constant pressure inflows, (ii) constant volume inflows, (iii) a modulated inflow rate or (iv) pulsed inflows to move the expandable structure 112 from a non-expanded condition to an expanded condition over an interval greater than about one tenth of a second. More specifically, the method includes moving the structure 112 from a non-expanded condition to an expanded condition over an interval ranging between about 1/10 of a second and 10 minutes, and more preferably between about 1 second and 5 minutes; and more preferably between about 10 seconds and 2 minutes.

In another aspect of the method of FIGS. 9A-9C, the system uses a controller to expand the expandable structure 112 to a first increased transverse dimension (while rotationally abrading bone) and then expansion forces are terminated with the structure partially expanded—followed by at least one other interval to expand the structure to a second transverse dimension and then termination of expansion again while rotationally abrading bone. This method further insures that no explosive expansion forces are applied within a vertebral body as occurs with a kyphoplasty-type balloon and method. Stated another way, the method of the present invention allows for expansion of structure 112 in a plurality of intervals to increased dimensions that are a fraction of the most-expanded shape of the expandable structure 112 (FIGS. 9A-9C). For example, the expandable structure 112 can be expanded to 10%-50% of its maximum working volume after which inflows are terminated. Then the structure can be expanded to 20%-60% of its maximum working volume followed by a non-expansion interval, then the structure can be expanded to 30%-70% of its working volume followed by a non-expansion interval, and so forth. During the above steps of the method, the controller can rotate the structure 112 at a selected rpm or a varied rpm within the ranges described above.

In another aspect of the apparatus and method depicted in FIGS. 8 and 9A-9C, the system uses fluid expansion to move an expandable structure from a first transverse dimension to a second greater transverse dimension in cancellous bone of a vertebra at low non-explosive fluid inflow pressures while rotationally abrading the cancellous bone. The pressures can be less than 100 psi, or more preferably less than 50 psi, or more preferably less than 25 psi. The system pressures used by the inventive method are far lower than practiced in balloon procedures adapted to crush and compact cancellous bone.

In one aspect, a method of the invention comprises inserting an expandable structure into cancellous bone, and expanding the structure at a selected rate of expansion without compacting the cancellous bone by rotation of an abrasive surfaced structure to thereby cut bone. In another aspect of the invention, the method of the invention includes inserting an expandable structure into cancellous bone, and expanding the structure step-wise to insure that explosive expansion does not occur together with the rotational bone abrading step. In another aspect of the invention, the method includes inserting an expandable structure into cancellous bone, and expanding the structure with fluid inflow pulses that range from 1 Hz to 1,000 Hz to enhance bone abrasion with the surface of the expandable structure. More preferably, the fluid inflows are pulses in the range of 10 to 100 Hz.

In one aspect, the apparatus of the invention for abrading bone comprises (a) an elongated member having a first end and a second end, (b) the second end having an expandable cross-section with an abrasive surface, and (c) a rotational drive mechanism coupled to the first end for rotation thereof to abrade a path or a space in a bone. In an exemplary embodiment, the abrasive surface is a polymeric material with abrasive particles affixed thereto, such as diamond particles. The diamond particles can be natural monocrystalline diamond, synthetic monocrystalline diamond, polycrystalline diamond or a combination thereof. The diamond particles have a mean dimension ranging from about 1.0 micron to 100 microns.

FIGS. 10A and 10B illustrates another cutting system and method for cutting a plane P in bone to assist in reducing a vertebral fracture that has healed to some extent. FIG. 10A depicts a bone cutting system 200 with introducer 205 that extends along axis 215 to working end 220 that includes first and second flexible rotational abrading (cutting) elements 222 a and 222 b. The system includes a rotation mechanism 225 in a handle (not shown) of the device such as an electric motor for rotating the rotational elements 222 a and 222 b. Each rotational element 222 a and 222 b has a proximal end 224 a and 224 b that is coupled to the motor drive and extends through a sleeve 226 a and 226 b in the introducer 205. As described above, the rotational elements 222 a and 222 b can be flexible metal wires, braided wires or braid-reinforces polymeric members. The system 200 further includes a reciprocating actuator member 240 for outward flexing of the distal end of the rotational elements 222 a and 222 b as shown in FIG. 10A. As can be seen in FIG. 10A, the distal ends 242 a and 242 b of the rotational elements are rotatable and secured in collar 244 that is coupled to actuator member 240. Still referring to FIG. 10A, it can be seen that the cutter 200 can be introduced into a bone in a reduced cross-sectional configuration with the cutting elements 222 a and 222 b in a linear configuration (phantom view). It further can be seen that simultaneous rotation of the cutting elements 222 a and 222 b and actuation by actuator member 240 will allow outward cutting in a plane in cancellous bone. FIG. 10B illustrates a method of use wherein the system is used to cut a more-or-less horizontal or sagittal plane P in the cancellous bone and can further be used to abrade cortical bone. Thus, the cutting system 200 can be used to create a weakened plane in the bone for enhancing the application of forces in vectors more-or-less perpendicular to the cut plane. Irrigation and aspiration can be used with the cutting system 200. The application of forces can be created by the inflow of a bone cement, by injection of graft material, by the expansion of a balloon, the injection of filler material into a knit, woven or braided structure or sac, or the use of a mechanical jacking system.

In the embodiment of FIG. 10A, the cutting elements 222 a and 222 b are indicated as flexible rotating members. In order to make the cutting elements 222 a and 222 b flex more controllably in the desired plane, further structure can be added to the working end as indicated in FIG. 11 which is a cut-away schematic view of a transverse section of the flexible portion of cutter 222 a (see FIG. 10A). In the embodiment of FIG. 11, a rotatable sleeve 222 a rotates around a flexible rod indicated as a flexible rectangular support member 245. The rectangular support member 245 is less adapted to deflect in use since the member 245 does not rotate. Other similar non-rotating support members can be used that are eternal to the rotatable sleeve 222 a and coupled to the sleeve by flanges.

In any of the above methods, the volume of bone cement volume can comprise a PMMA, monocalcium phosphate, tricalcium phosphate, calcium carbonate, calcium sulphate and hydroxyapatite, or any combination thereof. The bone cement also can carry allograft material, autograft material or any other infill bone infill granular material or scaffold material as in known in the art.

The above description of the invention intended to be illustrative and not exhaustive. A number of variations and alternatives will be apparent to one having ordinary skills in the art. Such alternatives and variations are intended to be included within the scope of the claims. Particular features that are presented in dependent claims can be combined and fall within the scope of the invention. The invention also encompasses embodiments as if dependent claims were alternatively written in a multiple dependent claim format with reference to other independent claims. 

1. A method of reducing a vertebral fracture, comprising: introducing a cutting system into a vertebra; cutting a substantially horizontal plane in at least one of cancellous bone and cortical bone thereby creating a weakened plane; and applying forces substantially perpendicular to the weakened plane to reduce the vertebral fracture.
 2. The method of claim 1, including cutting the plane with a rotating abrasion member.
 3. The method of claim 1, including cutting the plane with an elastomeric, rotating cutting member.
 4. The method of claim 1, including cutting the plane with a tissue-selective cutting member.
 5. The method of claim 1, wherein cutting the plane is accomplished at from 500 to 400,000 rpm.
 6. The method of claim 1, including cutting the plane with an expandable cutting member.
 7. The method of claim 1, further comprising flowing a fluid into the vertebra.
 8. The method of claim 7, further comprising aspirating the fluid and bone debris from the vertebra.
 9. A bone treatment device, comprising: an elongated assembly having a working end carrying at least one flexible rotatable member having an abrasive surface, the least one flexible member moveable between a first linear shape and a second curved shape; a rotation mechanism operatively coupled to rotatable member.
 10. The bone treatment device of claim 9 further comprising an actuation mechanism for moving the flexible member between the first linear shape and the second curved shape.
 11. The bone treatment device of claim 9 wherein the rotation mechanism is capable of rotating the flexible member at from 500 rpm to 400,000 rpm.
 12. The bone treatment device of claim 9 further comprising a fluid source coupled to a lumen in the elongated assembly.
 13. The bone treatment device of claim 9 further comprising an aspiration source coupled to a lumen in the elongated assembly.
 14. The bone treatment device of claim 9 further comprising a controller for controlling the rotation of the at least one flexible member. 